Rock Products

MAR 2013

Rock Products is the aggregates industry's leading source for market analysis and technology solutions, delivering critical content focusing on aggregates-processing equipment; operational efficiencies; management best practices; comprehensive market

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LOADING HAULING Driving Forward: Choosing an Articulated Truck CHALLENGE Evaluating articulated trucks based on engine choice. SOLUTION SCR technology is a possible consideration. TIP If the truck���s duty cycle is not high enough, then active regeneration serves as a backup system. By Rick Zettler There are a number of considerations when purchasing articulated haul trucks for your operation. Truck capacity, loading capabilities, hauling distance, road conditions and dump cycle times are just a few elements that are traditionally analyzed to determine the cor��� rect number and size of trucks to increase productivity and efficiency and reduce oper��� ating costs. With the recent change to ultra���low sulfur diesel (ULSD) fuel and the reduction of nitro��� gen oxide (NOX) emissions to meet Tier 4i/Stage III B standards, selecting the right engine technology for the application must also figure into the equation. There are two very different approaches to meet Tier 4i/Stage IIIB emission standards. Exhaust gas recirculation (EGR) recirculates a measured amount of exhaust gas with incom��� ing air to reduce NOX levels and requires a diesel particulate filter (DPF) to reduce par��� ticulate matter. The second alternative, selec��� tive catalytic reduction (SCR) uses diesel exhaust fluid (DEF; also known as AdBlue) to convert NOX into a harmless mixture of nitro��� gen vapor and water. ���At Scania, we have experience with both SCR and EGR technologies used in on���road trucks,��� said Peter Sundell, project manager, applica��� tion engineering for Scania CV AB, manufac��� turers of the Tier 4i/Stage IIIB engines powering Terex articulated dump trucks. Ken Emmett, truck product manager for Terex Construction Americas, added, ���As far as ap��� plication rules of thumb go, SCR technology will provide a better solution for engines above 325 hp (242 kW) and operated at a low duty cycle (below 50 percent). EGR technol��� ogy is better suited for lower horsepower en��� gines operating in high duty applications.��� EGR Analyzed Since EGR pumps oxygen���depleted exhaust back into the engine to reduce NOX emissions, the engine works a little harder. ���To get the same power out of the engine, its size is also increased,��� says Emmett. Additional engine components increase the system���s complexity and require more space under the hood. The engine requires larger cooling systems and a turbocharger specifically configured for the EGR solution to make up for the lack of oxygen in the exhaust. Up to 30 percent of oxygen���depleted exhaust is recirculated, which then must be cooled in order for emis��� sions to be removed. The EGR engine often re��� quires a diesel oxidation catalyst (DOC), which interacts with diesel fuel to oxidize pol��� lutants before they exit the system. These lower combustion temperatures re��� duce NOX but result in an increase in particu��� late matter. This matter is trapped in the DPF and, by regeneration, is oxidized into nitrogen gas and carbon dioxide and expelled through the exhaust pipe. The regeneration process increases the heat in the exhaust system to burn off the particulate matter. There are two methods of regeneration in today���s engines: passive and active. The pri��� mary is passive regeneration, which occurs during normal engine operating conditions, depending on the duty cycle, and is the most fuel���efficient method for cleaning the DPF. This process does not impact machine operation and does not require operator in��� volvement. If the truck���s duty cycle is not high enough, then active regeneration serves as a backup system. ���This only occurs when passive re��� generation is not possible, based on tempera��� 32 ROCKproducts ��� MARCH 2013

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